1. Field of the Invention
The present invention relates to a portable display system in which document data, such as electronic document or electronic magazine, is displayed on a display unit. The present invention relates to a display control method that controls the display system. Further, the present invention relates to a computer readable medium that stores display control program code instructions for use in the display system.
2. Description of the Related Art
A portable display system in which a document data, including characters and images, is displayed on a display unit, such as a liquid crystal display, is known. The proliferation of such portable display systems is increasing with development of a large-size liquid-crystal display and reduction of the cost. By using a portable display system, the user can easily display and view the information of electronic documents or electronic magazines, on the screen of the display unit.
For example, the electronic document format and the EPWing format are commonly used when displaying a text-based electronic document on the display unit. When displaying text data in the electronic document format, the frame of a viewer software package, which is configured to be analogous with a book, appears on the screen of the display unit. The original text data is converted into a processed document data using preset character fonts of the viewer software, and the processed document data is displayed. The electronic document format is primarily used when displaying text-based electronic documents. The EPWing format is similar to the electronic document format. When displaying text data in the EPWing format, the frame of a viewer software package appears on the screen of the display unit. The viewer software package is provided with a search engine. A desired part of electronic document is searched from the original text data, and the obtained part is converted into a processed document data, and the processed document data is displayed. The EPWing format is primarily used when displaying text-based electronic dictionaries.
On the other hand, when displaying a document data in which characters and images, such as drawings or illustrations, coexist, the PDF (portable document format) is frequently used. The PDF is a well-known file format for creating and viewing documents, which is originally developed to standardize Internet-based documents. The PDF file format includes the document data with data elements arranged according to a page layout. The document data with the page layout is visualized on the display unit. The PDF is primarily used when displaying text/image-mixed electronic magazines, including the document design, the page layout and the image data, on the screen of the display unit.
However, when an electronic document or electronic magazine is displayed using a portable display system, the screen of the display unit in the portable display system is too small in size to clearly view the details of the electronic document. When the entire document data with the original display size is selected on the portable display system, it is often difficult for the user to view the fine characters in the document data on the display unit.
Further, when an enlarged view of the document data is selected on the portable display system, the entire document data is enlarged on the display unit. In order to find out a desired part of the document data, it is necessary for the user to shift or scroll the enlarged view on the display unit by additionally manipulating the display system, which will be detrimental to the portability of the display system. In addition, when the enlarged view of the document data is displayed on the screen of the display unit, the entire document data with the original display size does not appear simultaneously with the enlarged view, which lowers the document displaying capabilities of the display system.